It is apparent that defect density bands appear at the location of the 4H polytype in this example of an asymmetric sandwich model 6H + 4H + 1DD + 6H, as observed by the darker contrast in this vicinity of the 5270 reflection. It should not therefore be surprising that a 90 m m thick region of 1DD exists, as deduced from reflection widths not adding up to the gap width, sandwiched between the more substantial 6H polytypes measuring 620 m m and 350 m m in thickness. The gap between the contributions of the 6H polytypes to the 3142 reflection has been measured as 140 m m of which only 50 m m can be attributed to the 4H polytype. The remainder is believed to be a disordered layer totalling 90 m m. In this example the crystal thickness was measured as 1020 m m, with streaking evident again along the 314l diffraction row to support the 1DD argument.

Originally it was difficult to differentiate between the two models shown below to distinguish the exact location of the 4H polytype. But on closer inspection the positioning of the 4H polytype against the upper of the 6H polytypes was made on the basis of the enlargement of the region shown in the figure. This shows the 3146 6H polytype in superpostion with the 3144 4H polytype and their relative spatial coalescence is evident.